The fabrication of a semiconductor device involves a plurality of discrete and complex processes. The semiconductor substrate typically undergoes many processes during the fabrication process. As a substrate is being processed, the substrate is typically clamped to a chuck. This clamping may be mechanical or electrostatic in nature. The electrostatic chuck traditionally consists of a plurality of layers. The top layer, also referred to as the top dielectric layer, contacts the substrate, and is made of an electrically insulating or semiconducting material, since it produces the electrostatic field without creating a short circuit. To create the electrostatic force, a plurality of electrodes may be disposed beneath the top dielectric layer. The plurality of electrodes is constructed from an electrically conductive material, such as a metal.
In certain applications, ion implantation may result in crystal defects and amorphization. This crystalline damage can often be restored by thermal processing, known as annealing. However, for certain high dose implants and device structures, typical post-implant annealing may not be sufficient to restore all the damage caused by the implantation. Heating the substrate during the implant process is known to reduce damage to the substrate and to preserve more of the crystalline structure to facilitate regrowth during the anneal process.
Substrates are typically heated by contact, such as through the use of a gas trapped between the workpiece and the chuck, such as when the substrate is held in place by electrostatic forces. The substrate may also be directly heated by the chuck. In both embodiments, heat is applied to the lower surface of the substrate by the chuck. Thus, the chuck is maintained at an elevated temperature to cause the substrate to be heated.
However, in certain embodiments, the heated chuck is in close proximity with a base. In certain embodiments, the heated chuck may be about ⅜″ thick, and may be heated to about 500° C. or more. The base may also be about ⅜″ in thickness and may be at or near room temperature through the use of water cooling.
The chuck and the base may be separated by about ⅛″ or less, such as through the use of ceramic washers, which are poor thermal conductors. The temperature difference between the heated chuck and the base may be hundreds of degrees. The base may act as a thermal sink, drawing heat from the chuck. In certain embodiments, a metal thermal shield is disposed between the heated chuck and the base. However, traditional metal thermal shields may be problematic. For example, because metal is an excellent thermal conductor, the metal thermal shield may be heated to nearly the temperature of the chuck. This may cause deformation of the metal thermal shield and possible contact between the metal thermal shield and the chuck or the metal thermal shield and the base. Because the chuck is typically made of ceramic materials, this may cause thermal stress to the chuck, which may lead to material fatigue or cracking.
It would be beneficial if there were a thermal shield that effectively thermally isolated the heated chuck from the base. Further, it would be beneficial if this thermal shield allowed the chuck and the base to be in close proximity without deforming.